1. Field of the Invention
The invention relates to calibration of laser-based workpiece micromachining and similar material processing systems, wherein the work-piece has considerable warpage or sag. The workpiece may be a semiconductor wafer, for instance a 300 mm wafer, with a thickness of a few hundred microns.
2. Background Art
The following representative patent references relate to various aspects of laser marking of wafers and electronic assemblies, illumination, and inspection/reading marks: U.S. Pat. Nos. 4,522,656; 4,945,204; 5,329,090; 6,309,943; 6,262,388; 5,929,997; 5,690,846; 5,894,530; 5,737,122; and Japanese Patent Abstract 11135390.
The following representative references provide general information on various laser marking methods and system configurations and components: “Galvanometric and Resonant Low Inertia Scanners”, Montagu, in Laser Beam Scanning, Marcel-Dekker, 1985, pp. 214–216; “Marking Applications now Encompass Many Materials”, Hayes, in Laser Focus World, February 1997, pp. 153–160; “Commercial Fiber Lasers Take on Industrial Markets”, Laser Focus World, May 1997, pp. 143–150. Patent Publications: WO 96/16767, WO 98/53949, U.S. Pat. Nos. 5,965,042; 5,942,137; 5,932,119; 5,719,372; 5,635,976; 5,600,478; 5,521,628; 5,357,077; 4,985,780; 4,945,204; 4,922,077; 4,758,848; 4,734,558; 4,856,053; 4,323,755; 4,220,842; 4,156,124.
Published Patent Applications WO 0154854, publication date 2Aug. 2001, entitled “Laser Scanning Method and System for Marking Articles such as Printed Circuit Boards, Integrated Circuits, and the Like” and WO0161275, published on 23Aug. 2001, entitled “Method and System for Automatically Generating Reference Height Data for use in a Three-Dimensional Inspection System” are both assigned to the assignee of the present invention. Both applications are hereby incorporated by reference in their entirety.
U.S. Pat. No. 6,501,061 discloses a method of determining scanner coordinates to accurately position a focused laser beam. The focused laser beam is scanned over a region of interest (e.g. an aperture) on a work-surface by a laser scanner. The position of the focused laser beam is detected by a photodetector either at predetermined intervals of time or space or as the focused laser beam appears through an aperture in the work surface. The detected position of the focused laser beam is used to generate scanner position versus beam position data based on the position of the laser scanner at the time the focused laser beam is detected. The scanner position versus beam position data can be used to determine the center of the aperture or the scanner position coordinates that correspond with a desired position of the focused laser beam.
There is a need in certain workpiece processing systems for calibration of multiple subsystems in three dimensions while facilitating on-line or off-line adjustment of laser processing parameters. Tolerance stackups within the system and workpiece may lead to poor mark quality or mark positioning errors. For instance, certain types of semiconductor wafers are being produced with an increasing number of die and finer feature dimensions, while decreasing thickness of wafers or similar workpieces have increasing surface variations due to sag and warpage.